Crawl Space Radon Mitigation in Roswell, GA

Sub-membrane depressurization for Historic Roswell cottages, East Roswell ranches, and Willeo custom homes

Effective radon reduction with moisture and air-quality benefits. Installation ranges $1,800 to $3,500.

Why Roswell Crawl Spaces Are Higher Risk

Direct Soil Exposure

Unlike slab homes where concrete provides some barrier, Roswell crawl spaces often have exposed dirt floors. Radon gas from the North Fulton granite below has a direct path into the home through the floor system above.

Historic Foundation Materials

Historic Roswell homes along Canton Street and in the Historic District often have stone, brick, or early concrete foundation walls with mortar that has weathered and settled over 100+ years. These walls have numerous small penetrations that allow radon entry.

Stack Effect

Older Roswell homes are often heated more aggressively in winter, creating strong stack effect. Warm air rising through the home creates negative pressure that draws soil gas through the crawl space into living spaces, concentrating radon during the heating season.

Multiple Entry Points

Crawl spaces combine exposed soil, foundation wall joints, utility penetrations, HVAC duct gaps, and spaces around plumbing. Each is a potential radon pathway. Without proper encapsulation and depressurization, all contribute to indoor levels.

Sub-Membrane Depressurization Process

Crawl Space Assessment

We inspect your Roswell crawl space for access points, soil conditions, foundation wall types, existing vapor barriers, and overall layout. For Historic Roswell homes we document any original stone or masonry foundation features before planning work.

Membrane Installation

A heavy-duty polyethylene membrane (minimum 6 mil, typically 12-20 mil for durability) is laid over the entire crawl space floor and sealed to foundation walls. Seams overlap and are taped. In Historic Roswell homes we use caulking compatible with stone and brick foundations.

Suction Point and Piping

One or more suction points are cut beneath the membrane. A PVC pipe routes from below the membrane through the crawl space and above the roofline. For historic homes we route through rear-facing walls or interior chases to preserve the front elevation.

Seal and Verify

All membrane edges and penetrations are sealed. An inline fan creates continuous negative pressure beneath the membrane, capturing radon before entry. A post-installation test confirms levels below 4.0 pCi/L (typically well below 2.0).

Roswell Crawl Space Areas We Serve

Historic Roswell District

Many pre-1950 homes in the Historic District have partial crawl spaces, sometimes combined with small basements. Foundations are often stone or brick with weathered mortar. These homes frequently test above 6 pCi/L.

Canton Street / Roswell Square

Older cottages and converted residential properties along the Historic District commercial edge often have shallow crawl spaces with limited access. Mitigation requires careful planning for equipment access.

Crabapple / Old Milton Border

Rural-style older homes near the Crabapple and Milton border often have crawl spaces, some with dirt floors that have never been sealed. These benefit significantly from sub-membrane depressurization.

East Roswell (older sections)

Mid-century ranch-style homes in sections of East Roswell often have crawl space foundations with original vapor barriers that have deteriorated or were never sealed to the walls.

Willeo / Mountain Park

Custom homes in Willeo and along Mountain Park often have split foundations with basement and crawl space sections. The crawl portions sit closer to granite bedrock and need focused mitigation.

Crawl Space vs. Other Foundations

Foundation	Cost	System	Why Different
Crawl Space	$1,800 - $3,500	Sub-Membrane Depressurization (SMD)	Membrane installation adds significant material and labor. Historic Roswell homes may also need preservation-aware routing.
Slab-on-Grade	$1,100 - $2,000	Sub-Slab Depressurization (SSD)	No membrane needed. Core through slab, install pipe and fan. Much simpler installation.
Basement	$1,200 - $2,500	Sub-Slab Depressurization (SSD)	Similar to slab but may have longer pipe runs. Finished basements add complexity.
Combination	$2,500 - $4,500	Multi-Point System	Both SSD and SMD techniques. Multiple suction points for different foundation sections.

Benefits Beyond Radon Reduction

Radon Reduction

The primary goal. Sub-membrane depressurization captures radon from the soil before it enters the home. Reduces radon levels by up to 99%, typically below 2.0 pCi/L.

Moisture Control

A sealed membrane prevents ground moisture from entering the crawl space. With the fan creating negative pressure, moisture is actively drawn away. Roswell homes often notice reduced musty odors after installation.

Pest Deterrent

A sealed membrane creates a physical barrier against insects, rodents, and other pests that would otherwise enter through exposed soil.

Indoor Air Quality

Crawl space air contributes to home air quality via the stack effect. Encapsulation and depressurization improve air quality throughout the house.

Energy Efficiency

Reducing moisture load and uncontrolled air infiltration from the crawl space helps HVAC run more efficiently. Some Roswell homeowners notice improved first-floor comfort.

Structural Protection

Chronic crawl space moisture damages floor joists and subflooring over time. The membrane and depressurization system protect these structural components.

Roswell Crawl Space FAQs

Why does crawl space mitigation cost more than slab?

Crawl space mitigation requires installing a heavy-duty polyethylene membrane across the entire crawl space floor and sealing it to the foundation walls before depressurization can work. For Roswell crawl spaces this membrane installation is the primary driver of added cost: more material, more labor, and physically demanding work in low-clearance spaces. Historic Roswell stone foundations also need specialized sealant.

Can I use my existing vapor barrier for radon mitigation?

In most cases, no. The 6-mil vapor barriers commonly found in Roswell crawl spaces were installed for moisture, not radon. They have gaps, seams that are not taped, and edges that are not sealed to the walls. For radon mitigation we install new, heavier membrane (typically 12-20 mil) with sealed seams and edges. In rare cases an existing barrier in excellent condition can be upgraded by sealing gaps and edges.

How long does crawl space mitigation take in a Roswell home?

A typical Roswell crawl space mitigation takes 6 to 10 hours, usually a single day. Larger crawl spaces, difficult access, multiple suction points, or the need to remove old materials can extend the timeline. Historic Roswell homes with stone foundations may take longer due to careful sealing work around original masonry.

Does crawl space encapsulation replace radon mitigation?

No. Encapsulation (sealing the space with a vapor barrier) helps with moisture but is not sufficient for radon reduction on its own. Radon mitigation requires active depressurization: a sealed membrane plus a fan creating negative pressure beneath the membrane. Encapsulation without active depressurization can actually concentrate radon under the membrane.

Will mitigation help with moisture in my Roswell crawl space?

Yes. The sealed membrane and continuous depressurization system addresses moisture as a secondary benefit. By sealing the soil and creating negative pressure beneath the membrane, ground moisture is significantly reduced. Many Roswell homeowners notice less musty odor, lower crawl space humidity, and reduced condensation after installation.

My Historic Roswell home has a stone foundation. Can it be mitigated?

Yes. Stone and brick foundations common in Historic Roswell can be successfully mitigated with sub-membrane depressurization. We use sealants compatible with historic masonry and avoid any work that would damage original materials. The membrane is sealed to the foundation wall using appropriate techniques for the specific material.

How does North Fulton clay soil affect radon in crawl spaces?

North Fulton clay holds moisture, and moist soil carries radon more effectively. Clay can also crack during dry periods, creating pathways for radon gas to migrate upward. Combined with the uranium-bearing Piedmont granite below Roswell, this makes crawl space mitigation particularly valuable in the area.

Can I combine mitigation with existing dehumidifier systems?

Yes. If you already have a crawl space dehumidifier, the radon mitigation system complements it. The sealed membrane reduces moisture load on the dehumidifier, and the depressurization system handles radon. Both can operate simultaneously. Some Roswell homeowners find their dehumidifier runs less after mitigation.